Historically, ClO2 has been commercially prepared by a reaction between a metal chlorate in aqueous solution, such as sodium chlorate (NaClO3), and a relatively strong acid such as sulphuric, phosphoric or hydrochloric acid.
Generally, processes for generating ClO2 make use an alkali chlorate-containing feedstock, usually NaClO3, that also includes a halide salt of alkali metal or other reducing agents. The sodium chlorate feedstock for such a ClO2 production process is typically generated by electrolysis of sodium chloride brine in any well-known manner. When chlorides are used as the reducing agent, the mixture of brine and chlorate is directly fed to one or more reactors where the feedstock contacts a desired acid and reacts to form ClO2. Due to the high amount of acidity required, e.g. 5-10N acid, coupled with the need for a reducing agent, small scale production of ClO2 from NaClO3 is not practiced. Examples of ClO2 generation processes via electrochemical or catalytic reduction of sodium chlorate in strong acid are reported for example in U.S. Pat. Nos. 4,501,824, 426,263, 4,381,290 and 4,362,707. These prior art teachings allow to dispense with the need for a separate reducing agent, still requiring however a chemical supply of acid in the process.